JPH03272413A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve a high distance measuring accuracy by varying a time constant of an integration circuit according to a distance and a reflection factor of a target object. CONSTITUTION:In the case of a short range or in the case of a large reflection factor of an object. A good condition is created with a higher level than a reference voltage 11 of amplification circuits 6a and 6b and limited noises in outputs of integration circuits 9a and 9b. In addition, outputs of voltage comparators 10a and 10b are not inverted and switches 13a and 13b are OFF. Then, in the case of a long range or a small reflection factor of the object, a condition with a bad signal/noise ratio is caused with an output voltage of the circuits 6a and 6b being lower than the voltage 11 and output voltages of the circuits 9a and 9b being low. Here, the outputs of the comparators 10a and 10b are inverted and the switches 13a and 13b are ON. Thus, integration time constants of the circuits 9a and 9b are reset for a larger value. By the contrary, the integration time constants are set larger at an initial stage and them, the integration time constants are reduced when input levels of the comparators 10a and 10b exceed the voltage 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distance measuring device for measuring the distance to a target object, which is suitable for optical equipment such as photography.

(Prior Art) Conventionally, various signal processing circuits have been proposed for distance measuring devices that measure the distance to a target object, and an example thereof will be described with reference to FIG. 3.

In this figure, numeral 1 denotes a light emitting circuit that drives a light emitting element 2. As shown in FIG. The light emitting circuit 1 and the light emitting element 2 constitute a light emitting means that emits light toward a target object 3 to be measured, and the light emitting element 2
The light from the target object 3 is configured to be irradiated onto the target object 3.

4a and 4b are light-receiving circuits that convert light into a signal voltage and amplify it, each having light-receiving elements 5a and 5b that receive reflected light from the target object 3 and convert it into a voltage signal; the light-receiving circuits 4a, Reference numeral 4b constitutes a light receiving means for receiving reflected light from the target object 3 and photoelectrically converting it. Reference numerals 6a and 6b denote amplifier circuits, which receive optical information signals outputted from the light receiving circuit 4a and the light receiving circuit 4b, respectively, and amplify their outputs. 7 is a waveform processing circuit, which includes amplifier circuits 6a and 6b.
Compute using the output from as input. 8 is distance information.

Next, the operation will be explained.

The light emitted from the light emitting element 2 driven by the light emitting circuit 1 hits the target object 3 and is reflected to the light receiving element 5a,
Enter 5b. The light entering the light receiving elements 5a and 5b is converted into a signal voltage and amplified by the light receiving circuits 4a and 4b, respectively.

Next, the optical information signals output from the light receiving circuits 4a and 4b are amplified by the next-stage amplifier circuits 6a and 6b, respectively, and then input to the waveform processing circuit 7, where calculations are performed to calculate the distance. and output as distance information 8.

[Problem to be solved by the invention]

Since the signal processing circuit of the conventional distance measuring device is configured as described above, the light intensity incident on each of the light receiving elements 5a and 5b varies depending on the distance to the target object 31 and the reflectance, etc.
The signal may be weak, and in this case, even if it is amplified by the amplifier circuits 6a and 6b as usual, noise will occur, making it difficult to amplify only the true optical signal, and the signal-to-noise ratio (S/N
) was getting worse. Then, the noise generated by the light receiving circuits 4a, 4b and the amplifier circuits 5a, 5b is added to the optical signal voltage, so as a result, especially when the optical signal is weak (for example, at a long distance or when the subject reflectance is low) However, there was a problem in that the ranging performance deteriorated.

This invention was made to solve the above problems, and even when the optical signal is weak, the signal-to-noise ratio (
It is an object of the present invention to provide a distance measuring device that can improve the S/N ratio and the distance measuring accuracy.

[Means for Solving the Problems] A distance measuring device according to the present invention includes: a light emitting device that emits light toward a target object; a light receiving device that receives reflected light from the target object and photoelectrically converts the received light; and the light receiving device. an amplifier circuit that amplifies the optical information signal from the amplifier circuit, a voltage comparator that compares the output voltage of this amplifier circuit with a reference voltage, an integration circuit whose integration time constant changes depending on the output of this voltage comparator, and It is equipped with a waveform processing circuit that calculates distance information by calculating the output from the integrating circuit.

[Effect]

In this invention, the input level from the amplifier circuit to the voltage comparator is compared with a reference voltage, and the integration time constant of the integration circuit is changed in accordance with the comparison result.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a signal processing circuit of a distance measuring device according to the present invention.

In this figure, the same reference numerals as in the conventional one shown in FIG. 3 are the same, and the explanation thereof will be omitted.

9a and 9B are integral circuits whose time constants can be switched manually using the outputs of the amplifier circuits 6a and 8b, respectively; 10a;
A voltage comparator 10b receives the outputs of the amplifier circuits 6a and 6b, compares it with a reference voltage 11, and is set so that the output changes when the optical signal is weak. 12
is an AND gate, which operates switches 13a and 13b to increase the integration time constant of integration circuits 9a and 9b when the optical signals are weak in both channels, that is, when the outputs of amplifier circuits 6a and 6b are small. .

Next, the operation of the signal processing circuit of the present invention will be explained with reference to FIG.

FIGS. 2(a) to 2(f) are explanatory diagrams of the operation of FIG. 1, with the horizontal axis representing time and the vertical axis representing the output voltage v6a+ of the amplifier circuits 6a and 6b.
V6bx integration circuit 9a, 9b output voltage V911+
The on/off states of vob and switches 13a and 13b are shown.

First, a case where the optical signal is large (at a short distance or when the object reflectance is large) will be explained.

In this case, the reference voltage 11 of the amplifier circuits 6a and 6b is higher (FIG. 2(a)), and the outputs of the integrating circuits 9a and 9b are also in a good state with less noise (FIG. 2(b)). , the outputs of voltage comparators 10a and 10b are not inverted, and switch 1
3a and 13b are in the off state (FIG. 2C)).

Next, a case where the optical signal is small (at a long distance or when the object reflectance is small) will be explained.

In such a case, the output voltages of the amplifier circuits 6a and 6b are lower than the reference voltage 11 (FIG. 2(d)), and the output voltage of the integrator circuit 9a
, 9b is low, resulting in a poor signal-to-noise ratio (FIG. 2(e)). At this time, voltage comparator 10
The outputs of the terminals g and 10b are inverted, and the switches 13a and 13b are turned on (FIG. 2(f)).

That is, by turning on the switches 13a and 13b in this way, the integrating circuit 9a.

The integration time constant of 9b is reset to a larger value.

Therefore, as shown in the second half of FIG. 2(e), the outputs of the integrating circuits 9a and 9b have an improved signal-to-noise ratio (S/N), facilitate waveform processing, and improve distance measurement accuracy. improves.

In the above embodiment, the integration time constants of the integration circuits 9a and 9b are set to 1 in the initial state, but conversely, the integration time constants are increased in the initial state, and the voltage comparator 1
It is also possible to configure the integration time constant to be small when the input level of 0a and 10b becomes equal to or higher than the reference voltage 11.

〔Effect of the invention〕

As explained above, the present invention includes a light emitting means for emitting light toward a target object, a light receiving means for receiving reflected light from the target object and photoelectrically converting it, and amplifying an optical information signal from the light receiving means. An amplifier circuit, a voltage comparator that compares the output voltage of this amplifier circuit with a reference voltage, an integrator circuit whose integration time constant changes depending on the output of this voltage comparator, and an output from this integrator circuit that calculates the output voltage. Since it is equipped with a waveform processing circuit that calculates distance information, the time constant of the integrating circuit can be changed according to the distance 1 reflectance of the target object (subject), and the signal-to-noise ratio (S/N) This has the effect that a good state of distance measurement can be maintained and distance measurement accuracy can be improved. Furthermore, since the circuit configuration is simple, manufacturing is easy, especially when applied to an integrated circuit, and it is suitable for mass production, so it is possible to prevent cost increases.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the distance measuring device of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is a block diagram of a signal processing circuit of a conventional distance measuring device. . In the figure, 1 is a light emitting circuit, 2 is a light emitting element, 3 is a target object, 4a, 4b are light receiving circuits, 5a, 5b are light receiving elements, 6
a, 6b are amplifier circuits, 7 is a waveform processing circuit, 8 is distance information, 9a, 9b are integration circuits, 10a, TOb are voltage comparators, 11 is a reference voltage, 12 is an AND gate, 13a, 13
b is a switch. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A light emitting means for emitting light toward a target object, a light receiving means for receiving reflected light from the target object and photoelectrically converting it, an amplifying circuit for amplifying an optical information signal from the light receiving means, and an output voltage of the amplifying circuit. A voltage comparator that compares the voltage with a reference voltage, an integrating circuit whose integration time constant changes depending on the output of this voltage comparator, and a waveform processing circuit that calculates distance information by calculating the output from this integrating circuit. A distance measuring device characterized by comprising: